It is conventional practice in the production of solid gypsum products to employ an aqueous slurry composed predominantly of "calcined" gypsum, which slurry is poured or formed into the desired shape of the final product and is then cured and dried. Calcined gypsum is one term customarily used in this field to denote calcium sulfate hemihydrate, CaSO.sub.1 .multidot.1/2H.sub.2 O. Aqueous slurries of calcined gypsum are fluid and gradually react with the water in the slurry to form hydrated calcium sulfate, CaSO.sub.4 .multidot.2H.sub.2 O, which is solid. The aqueous slurry of calcined gypsum conventionally contains functional additives such as accelerators, fibers, colorants, starches, and the like. This slurry also often contains small particles of hydrated calcium sulfate which serve as "seeds", i.e., nucleation sites.
Construction products such as gypsum board are a familiar example of products formed using aqueous slurries of calcined gypsum. The board is typically formed by depositing an aqueous slurry of calcined gypsum and other desired additives onto a horizontal substrate, typically heavy paper, which is destined to be one surface of the finished wall board product, following which a second sheet of heavy paper or the like is placed over the flat slurry to form a sandwich which is subsequently treated to dry and solidify the final wallboard product.
In the production of gypsum board, and in the production of other articles from aqueous slurries of calcined gypsum, it is known to incorporate a surfactant component and to subject the water borne surfactant to foaming, before, during or after combination with the calcined gypsum. In this way, the slurry contains entrained air. Foaming techniques of this type have been found to provide advantages such as reduced consumption of calcined gypsum for a given quantity of final product, and accordingly reduced weight of the final product, while retaining a generally satisfactory level of strength in the final, dried product.
Foaming techniques of this type are disclosed in published patent application WO 95/16515, which discloses foaming agent compositions comprising alkyl sulfate and alkoxylated alkyl sulfates; U.S. Pat. No. 5,466,393, which discloses foaming compositions comprising a glycol species selected from alkylene glycols, alkylene glycol ethers and polyalkylene glycol ethers, mixed together with alkylpolyether sulfates; CA 124:183886q which discloses foaming agents containing polyoxyethylene monoalkylether sulfate ester salts and ethoxylated lower alkanols; and U.S. Pat. No. 5,158,612 which discusses narrow range alkoxylated alcohol sulfonates as well as U.S. Pat. No. 4,168,370 which discusses sodium and ammonium salts of alcohol ether sulfates.
There remains a need for foaming compositions and processes useful in the preparation of foamed gypsum compositions, which afford improved strength, or greater weight reduction, and which employ readily available materials which are easily adaptable to such applications.